Mechanism Investigation of High-Performance Li-Polysulfide Batteries Enabled by Tungsten Disulfide Nanopetals

摘要

Understanding the reaction kinetics and mechanism of Li-polysulfide batteries is critical in designing advanced host materials for improved performance. However, up to now, the reaction mechanism within the Li-polysulfide batteries is still unclear. Herein, we study the reaction mechanism of a high-performance Li-polysulfide battery by in situ X-ray diffraction (XRD) and density functional theory (DFT) calculations based on a multifunctional host material composed of WS2 nanopetals embedded in rGO-CNT (WS2-rGO-CNT) aerogel. The WS2 nanopetal serves as a "catalytic center" to chemically bond the polysulfides and accelerate the polysulfide redox reactions, and the 3D porous rGO-CNT scaffold provides fast and efficient e(-)/Li+ transportation. Thus, the resulting WS2-rGO-CNT aerogel accommodating the polysulfide catholyte enables a stable cycling performance, excellent rate capability (614 mAh g(-1) at 2 C), and a high areal capacity (6.6 mAh cm(-2) at 0.5 C). In situ XRD results reveal that the Li2S starts to form at an early stage of discharge (at a depth of 25% of the lower voltage plateau) during the discharge process, and beta-S8 nucleation begins before the upper voltage plateau during the recharge process, which are different from the conventional Li-S battery. Moreover, the WS2 itself could be lithiated/delithiated during the cycling, making the lithiated WS2 (LixWS2, 0 = x = 0.3) a real host material for Li-polysulfide batteries. DFT calculations suggest that LixWS2 (0 = x = 0.3) exhibits moderate binding/anchoring interactions toward polysulfides with adsorption energies of 0.51-1.4 eV. Our work reveals the reaction mechanism of the Li-polysulfide batteries and indicates that the lithiated host plays an important role in trapping the polysulfides.